Methiozolin Rates and Timing for Poa Annua (L.) Control in Overseeded Turf in the Coachella Valley.

Methiozolin is under development in the United States for selective Poa annua control in creeping bentgrass putting greens. Both pre- and postemergence herbicide activity limit its use around the time of seeding desirable turfgrasses. A study was conducted in 2013-14 on golf courses in Palm Desert and Indian Wells, CA to evaluate methiozolin applied as single or sequential applications at 0, 0.5, 1.0, and 2.0 kg ha^-1 either 6 or 8 wks before overseeding (WBOS) or 6 to 12 wks after overseeding (WAOS) bermudagrass fairways with perennial ryegrass. Ethofumesate (SC vs. EC formulations), trinexapac-ethyl, paclobutrazol, and mesotrione were applied alone or in combinations between 6 and 16 WAOS. The product ReeVerse Poa (ReeCourse Golf, LLC) was also applied between 4 and 16 WAOS. Percent P. annua cover and ryegrass thinning were assessed visually throughout the study until transition to bermudagrass. Methiozolin applied after overseeding (postemergence) provided more effective P. annua control compared to applications before overseeding (preemergence). The safest and most effective methiozolin treatment was 1.0 kg ha^-1 applied sequentially at 10 and 12 WAOS. Overall, the safest and most effective control of P. annua was achieved with a tank-mix of ethofumesate, paclobutrazol, and trinexapac-ethyl applied 6 and 9 WAOS. ReeVerse Poa did not decrease P. annua populations. Our results indicated that methiozolin could be used for P. annua control in overseeded turf, but applications need to be delayed to prevent ryegrass injury and weed control is slower compared to conventional chemicals used for this purpose.